The heart of Sparus auratus: a reappraisal of cardiac functional morphology in teleosts

This study analyses the morpho-dynamic characteristics of the gilthead seabream (Sparus auratus) heart. Using in vitro heart preparations from small (52.5"2.6 g body weight, mean"S.D.) and large (257.14"9.68 g body weight, mean"S.D.) animals, changes in mechanical performance were studied under preload and afterload challenges. Small and large fish showed similar Frank-Starling response and maximum cardiac output of 66.5"4.6 and 55.66"4.54 mlyminykg body weight,respectively, obtained with corresponding input pressures of 0.7 kPa and 1 kPa. In small S. auratus hearts, stroke volume (SV) decreased at afterloads above 2.8 kPa. However, large hearts were able to maintain SV up to an afterload of 3.9 kPa. This hemodynamic flexibility and the intrinsically high chronotropism indicate that the ventricular pump is suited to produce pressure work,matching well the active locomotory characteristics of S. aurata. The morphologic study revealed entirely trabeculated pyramidal ventricles and a system of small luminae and trabecular sheets radiating outward from the central lumen. The ventricular periphery was exclusively formed by single trabeculae and corresponding lacunary spaces. The ventricular cavity was enclosed by an outer myocardial monolayer ‘shell’. Myofibril organization differed in the trabeculae and in the outer monolayer. In addition to their functional interest (e.g., nonuniform intracavitary stress distribution within the ventricular wall), the structural features challenge common beliefs regarding the typical ‘athletic’ fish heart design.